fix!: invalid JSON RPC internal error code

[jawid-h]

Issue being fixed or feature implemented

Updated return error code according to a spec here

What was done?

Updated return error code to a -32603 for internal errors

How Has This Been Tested?

Tested using running mn-bootstrap using custom pre-built dapi image. And checking error code returned by the dapi-client

Breaking Changes

Error code for internal errors now -32603, as per spec.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[shumkov]

Good catch! 👍